ABSTRACT
Monte-Carlo conformational searches with four kinds of force fields (AMBER94, MM3*, MMFFs, and OPLS-2005) were performed on glycylglycine (GlyGly), deprotonated glycylglycine (GlyGly(-)), glycylglycine chloride anion complex (GlyGly · Cl(-)), glycylglycine sodium cation complex (GlyGly · Na(+)) and glycylglycine dihydrate [GlyGly · (H2O)2]. Combined with Hartree-Fock (HF) and second-order Møller-Plesset (MP2) optimizations, conformations within an energy of 20 kJ mol(-1) were predicted. After MP2 calculations, the geometries and relative energies of the predicted structures were the same regardless of the force field used. Therefore, the performance of different force fields reflects mainly the conformational search process. For GlyGly, there was practically no difference among the four force fields. Due to the complex hydrogen bonding network when involving water, the total number of resulting conformers for GlyGly · (H2O)2 increased drastically. Moreover, the MMFFs force field fared best in finding the global minimum compared to the remaining three force fields. In describing hydrogen bonded and inter-molecular complexes, we recommend application of the MMFFs and AMBER94 force fields. Furthermore, the MMFFs and OPLS-2005 force fields have a good description of electrostatic interactions. This work will contribute to helping the reader make an optimal choice of force field, taking into account the latter's strengths and limitations.
Subject(s)
Chlorides/chemistry , Computer Simulation , Glycylglycine/chemistry , Models, Chemical , Models, Molecular , Sodium/chemistry , Water/chemistry , Energy Transfer , Glycylglycine/analogs & derivatives , Hydrogen Bonding , Monte Carlo Method , Protein Conformation , Static ElectricityABSTRACT
<p><b>AIM</b>To determining whether the level of serum leptin altered and whether the expression of leptin receptor immunoreactivity changed following taste stimuli.</p><p><b>METHODS</b>After intraoral infusions of chemical solutions, which included 3 mol/L sucrose, 5 mmol/L sodium saccharin, 0.1 mol/L NaCl, 0.01 mol/L HCl, 1 mmol/L quinine H2SO4 and 0.1 mol/L monosodium glutamate, serum leptin concentration were measured by using rat leptin RIA kit. Immunohistochemistry ABC method was used for brain sections with high-specify-goat antiserum against leptin receptors.</p><p><b>RESULTS</b>Comparing with the control group (intraoral infusion of distilled water), the level of serum leptin only in sweet group (sucrose an d saccharin) raised (P < 0.05). Many neuronal cell bodies and dendritic processes showed leptin receptors immunoreactivity (LR-IR) in many brain regions, such as amygdala, hypothalamus, parabrachial nucleus and nucleus of the solitary tract, which had intense relationship with taste and feeding. But the number of positive-stained cells showed no difference in aforementioned brain regions between the taste stimuli group and the control group.</p><p><b>CONCLUSION</b>After intraoral stimuli of sweet substances, the serum leptin concentration increased. LR-IR cells exist in amygdala which plays a critical role in the initiation and guidance of feeding. This findings led us study possible effects of leptin on taste responses. Probably, leptin influences food intake through the sense of taste.</p>
